Make a quarter curve with curves
Curves Circle method

Add &gt; Curve &gt; Circle,
In Edit mode go to Curve &gt; Control Points &gt; Set handle Type  and set it to to Free.
Then delete one knot point, and adjust the remaining knot and handles as in the image below.



A slight warning, this will only approximate a quarter curve, but often this will be sufficient for graphics.
Python script
Here is a short script that might be of interest to future python coders, creating this curve through code: https://gist.github.com/zeffii/5775583